PCT/JP03/05612 and PCT/JP03/13731, both unpublished as of the date of filing of this application, disclose a multi-antenna radio system in which a plurality of antenna units are connected to one base transceiver station in order to reduce radio dead zones inside buildings or in underground shopping areas and the like, by utilizing the characteristic that RAKE reception is possible in a CDMA (Code Division Multiple Access) system. At each antenna unit, the received signal is amplified by a variable gain amplifier and converted by an A/D converter into a digital signal. The plurality of antenna units and the base transceiver station are connected in series, the base transceiver station being located at one end (upstream end); in this configuration, the antenna unit located at the other end (downstream end) passes the digital signal of its received signal to its upstream adjacent antenna unit where the digital value of its received signal is added to the digital value of the received signal received from its downstream adjacent antenna unit, and the process is repeated from one antenna unit to the next, the base transceiver station thus receiving the sum of all the received signals. The base transceiver station reconstructs the signal for each channel by performing RAKE combining on the sum of the received signals for each spreading code.
In such a multi-antenna radio system, to make the most of the advantage that an arbitrary number of antenna units can be connected to one base transceiver station, it is desired that the gain of the variable gain amplifier in each antenna unit be automatically controlled so that the power value of the sum of the received signals that the base transceiver station receives will fall within an optimum range even when the number of connected antenna units changes.
Patent document 1: Japanese Unexamined Patent Publication No. 2003-152611
Patent document 1: Japanese Unexamined Patent Publication No. 2001-285158